1. Field of the Invention
The present invention generally relates to touch screens and, more particularly, to optical touch screens having signature capture capability.
2. Description of the Related Art
Touch screens and signature capture devices are well known on personal digital assistants, payment terminals, and portable computers designed for various markets. These touch/signature capture screens have made use of various technologies. Each of these, however, has some disadvantages.
The most common type of technology is found on hand-held personal digital assistants. These use flexible membrane technology that has not proven to be adequately durable for demanding commercial applications. In addition, the membranes are positioned over the display, reducing the brightness and contrast of the display.
Other technologies include capacitive sensors mounted on the screen, as well as infrared (IR) light emitting diodes (LEDs) positioned around the periphery of the screen. The most reliable of these is the IR sensor technology, which consists of an array of photosensors along two sides of a display, and a corresponding array of IR light sources, such as LEDs, along the opposite sides. The sensors detect when a finger or pen touches the screen by detecting that the IR light from the opposite LED is no longer visible to a sensor. While this kind of technology works well for sensing finger touches in applications such as automated teller machines, where high resolution of the location of the touch is not necessary, signature capture, while possible, requires such a dense population of sensors and LEDs as to become too expensive and to use too much power for some applications. In addition, custom arrays of LEDs and sensors have to be created for each size of screen that is to be accommodated.